High power diode laser arrays are now in use for a variety of technological applications. Commercially available diode array systems with high output power (greater than 1 watt) are currently relatively expensive. Although the cost of such systems is likely to decrease over time, a typical current cost for a 15 watt diode array is in the range of $25,000. Clearly, the users of such arrays wish to have as much usable laser light as possible. Unfortunately, much of the light that is emitted is not usable for many applications.
One important use of high power diode lasers is for producing laser polarized noble gases for medical magnetic resonance imaging (MRI). As an example, a 15 watt laser array can be used to optically pump the noble gas sample. The user tunes the array to a wavelength at which the gas in the cell is activated, e.g., 795 nanometers (nm) where rubidium is used. Unfortunately, like all high power diode laser systems now available, the laser not only puts out laser light at the desired 795 nm, but also a spread of wavelengths around 795 nm. While the peak of the spectrum may be at 795 nm, the 15 watts of output power is typically spread over several nanometers, typically displaying a Gaussian-type curve of laser power versus wavelength centered at the desired wavelength. Thus, only a fraction of the 15 watts of output power is usable by the cell. Under reasonably attainable conditions, generally only the light which is between about 794.9 and 795.1 nanometers is useful. The vast majority of the output power of the laser is outside this range and is wasted; typically of the 15 watts of power produced by the laser system, only 1 or 2 watts may fall within the useful range.